An apparatus for processing a sample including fibers and trash, having a cylinder rotating in a first direction for receiving the sample. At least one of said toolholder units comprises: a reaction structure, a precision structure destined to bear a bending tool, and elastic means positioned between the precision structure and the reaction structure and able to allow a movement of the precision structure relative to the reaction structure under the action of the bending load. The associated overlapping of the intake valve faces outside of a projection of the cylinder bore is utilized to form two symmetric flow masks which in turn function as the primary means for generating strong barrel swirl during the intake stroke.